New insight to the fission dynamics using α-particle emission as a probe

The α-particle energy spectra have been measured in coincidence with fission fragments over a wide range of relative angles with respect to fragment emission direction in 11B (62 MeV), 12C (69 MeV) + 232Th reactions. The α-particle multiplicity spectra have been fitted with moving source model to extract the pre-scission (αpre) and near-scission (αnse) components. The present results along with available data from literature over a wide range of Z2/A and excitation energy of compound systems, have been analyzed to develop certain global features of the pre- and near-scission emission characteristics. It is seen that αpre values when normalized to EC2N,3 (ECN is the compound nucleus excitation energy) show a systematic linearly increasing trend with α-particle emission Q-value (Qα). The fraction of near-scission multiplicity is observed nearly same at around 10% of the total pre-scission multiplicity for all the systems. In case of 12C + 232Th reaction, enhanced αnse is observed suggesting a new source of α-particle emission and it has been identified as due to 2-α breakup of 8Be produced in α-transfer induced fission events. When above α-particle multiplicity component for 12C + 232Th system is exclusively considered in moving source analysis the α-pre and αnse follow the present systematics. (author)